Apparatus for setting stitches of tubular knitted fabrics for deknitting

ABSTRACT

Apparatus for crimping and heat setting a deknittable knitted fabric of thermoplastic filaments under tension between hot toothed rolls, characterized by the provision of stitch loopdensity regulating means at at least two positions and a device for imparting a uniform tension to the fabric running between fabric feed rolls and the hot toothed rolls, whereby a uniform heat-setting effect is given to the fabric and the obtained yarns have an excellent crimp fastness.

United States Patent Koizumi et al.

1 5] Mar. 7, 1972 [54] APPARATUS FOR SETTING STITCHES OF TUBULAR KNITTED FABRICS FOR DEKNITTING [72] Inventors: Takao Koizumi; Takao Kaiita, both of Komatsu-shi, Japan [73] Assignee: Teiiin Limited, Osaka, Japan [22] Filed: Feb. 24, 1969 [21] Appl. No.: 801,477

[30] Foreign Application Priority Data Feb. 26, 1968 Japan ..43/12151 [52] US. Cl. ..26/69 R, 26/55 R, 28/1 .3, 28/1.8, 28/72.16

[51] Int. Cl..'. ..D06c 23/00, D02g 1/14, D02g 1/20 [58] Field ofSearch ..26/69,55,56;28/72.16, 1.3, 28/l.8, 72.11, 72 F1; 242/7551 [56] Reierenoes Cited UNITED STATES PATENTS 1,673,521 6/1928 Maas ..242/75.51 X 1,706,164 3/1929 Hull ..242/75.51

2,306,157 12/1942 Edwards et a1. ....242/75.51 2,109,469 3/1938 Cohn et a]. ..26/56 5 2,187,644 l/l940 Cohn et a1. ..26/56 2,192,880 3/1940 Cohn et a1. ..26/55 2,627,644 2/1953 Foster ..28/72 Fl" UX 2,842,828 7/ 1958 Allen et al. ..28/72 F1" UX Primary Examiner-Robert R. Mackey I AttomeySherman and Shalloway [57] ABSTRACT Apparatus for crimping and heat setting a deknittable knitted fabric of thermoplastic filaments under tension between hot toothed rolls, characterized by the provision of stitch loopdensity regulating means at at least two positions and a device for imparting a uniform tension to the fabric running between fabric feed rolls and the hot toothed rolls, whereby a uniform heat-setting effect is given to the fabric and the obtained yarns have an excellent crimp fastness.

2 Claims, 8 Drawing Figures APPARATUS FOR SETTING STITCI'IES OF TUBULAR KNITTED FABRICS FOR DEKNITTING This invention relates to apparatus for producing crimped yarns by knit-molding with the object of providing uniform crimps to knit-mold-type crimped yarns and increasing their crimp fastness by imparting a uniform heat-setting effect to a tubular knitted fabric. Knit-molded yarns are yarns formed by deknitting a synthetic tubular fabric which has been crimped and heat-set via toothed rolls and the like.

Heretofore, crimped yarns obtained by the knit-molding method have been low in their crimp fastness. In particular, knit-molded type crimped yarns of polyester are easily stretched under a low load, and do not return to their original state. It is therefore disadvantageous that a fabric made of such crimped yarns is stretched out by tension exerted during the knitting, weaving, scouring, or dyeing process, and therefore, there is no advantage at all in using crimped yarns.

We have made extensive studies in an attempt to remove these defects of the prior art, and found that during heatsetting of a tubular knitted fabric according to the prior art which is carried out in the absence of any external restraining force, the heat-setting of the said fabric by heat and the shrinkage by heat of the said fibers that constitute the fabric take place simultaneously, and moreover, the latter proceeds to a greater degree than the former, and that consequently, heat energy which is to be used for heat-setting of the fabric is wasted, resulting in the lowering of the heat-setting effect. We have therefore come 'to a conclusion that the shrinkage of fibers at the time of heat-setting should be restrained, and that if the heat-setting is conducted during the restraining of shrinkage while maintaining an external restraining force in the course and wale directions constant, most of the heat energy is consumed for heat-setting, and a uniform heat-setting effect can be obtained, and moreover, the crimp fastness of the obtained crimped yarns can be remarkably enhanced.

Turning to the prior method, we have found that a tubular knitted fabric produced for preparation of crimped yarns is very loose in its texture, and can be readily stretched in any direction such as wale direction, course direction, or a direction oblique thereto. For instance, when the fabric is placed under tension in a wale direction, the fabric stretches in that direction, but it contracts in a course direction. This means that the shape of the loops which form the tubular knitted fabric is deformed.

On the other hand, when the fabric is subjected to heatsetting under tension both'in a wale direction and a course direction, it is necessary to provide grasping means to pull the fabric in the course direction. Where such grasping means is utilized, the heat-setting effect of the grasped part of the fabric is reduced, and the crimp yarn has different heat-setting effects along the axis of the fibers. Thus, it can be appreciated that it is very difficult to exert a uniform tension on a tubular knitted fabric. Because of such difficulty, improvements of the prior process have not been made.

The first problem we took up is how to place a tubular knitted fabric to be fed into a heat-setting apparatus under an appropriate tension both in wale and course directions; more particularly, what should be done to prevent each of the loops that form the tubular knitted fabric from deforming at random. In the present invention, each of the loops is maintained in a uniform shape, i.e., uniform stitch density, at the time of heat-setting, and in this state, is subjected to a uniform appropriate tension in the advancing direction of the tubular knitted fabric, i.e., wale direction. This can be achieved by using a stitch loop density regulating piece for the former, and for the latter, by passing a tubular knitted fabric through an apparatus wherein a special tension device is suspended onto the running tubular knitted fabric which subsequently passes through hot toothed rolls, whereby a uniform heat-setting effect is imparted to the said tubular knitted fabric. Thus knitmolded type-crimped yarns having remarkably improved crimp fastness are obtained.

An object of the invention is to provide uniform crimps to knit-molded type crimped yarns and increase their crimp fastness by imparting a uniform heat-setting effect to a tubular knitted fabric for deknitting.

Another object of the invention is to provide crimped yarns by employing a stitch loop density regulating piece for a tubular knitted fabric running towards a heat-setting apparatus, and suspending a special tension device on the running tubular knitted fabric, whereby the yarns are heat-set in an appropriate restrained state.

The apparatus for practicing the present invention will be described by reference to the accompanying drawings in which:

FIG. 1 is a view illustrating the apparatus for heat-setting the stitches of a tubular knitted fabric for deknitting;

FIG. 2 is a view illustrating a means for imparting tension to a tubular knitted fabric;

FIG. 3 is a view illustrating another means for imparting tension to a tubular knitted fabric;

FIG. 4 (a) is a plan view of a stitch loop density regulating piece;

FIG. 4 (b) is a back elevation thereof;

FIG. 4 (c) is a side elevation thereof; and,

FIG. 5 (a) and (b) are views illustrating the function of the stitch loop density regulating piece.

Referring to the drawings, a tubular knitted fabric 1 of FIG. 1 is one prepared by a suitable knitting machine, preferably one knitted in cylindrical shape and flattened. The tubular fabric I is knitted from thermoplastic yams, such as polyester yarns, polyamide yarns, polyvinyl chloride yarns, polyacrylonitrile yarns, polyolefin yarns and acetate yarns.

The details of stitch loop density regulating pieces 8 and I4 shown in FIG. I are given in FIG. 4. The stitch loop density regulating pieces 8 and 14 are inserted in the tubular knitted fabric 1, and are maintained in a fixed position by a means such as supporting in a suspended state. These regulating pieces 8 and 14 are of a triangular shape as shown in FIG. 4 (a), preferably in the shape of an isosceles triangle. The shape of the rear and side surfaces of regulating pieces 8 and 14 are shown respectively in FIG. 4 (b) and FIG. 4 (c). It is preferable that each end of such regulating piece be rounded. In a plan view, this regulating piece is inserted in a tubular knitted fabric in a manner such that its base rides on supporting rods.

As shown in FIG. 5 (a), when the tubular knitted fabric is pulled in the direction of arrow A, it stretches in the wale direction, but contracts in the course direction. In order to remedy this, the regulating pieces 8 and 14 are inserted as shown in FIG. 5 (b) to expand the fabric in the course direction. At the same time, tension is imparted to the looplike yarns constituting the fabric 1 which are loosened in the I course direction. This is the most important. The regulating pieces 8 and 14 serve to maintain each of the loops of fabric in a uniform shape, and at the same time, impart a suitable tension to the looplike yarns. When such a regulating piece is not used, a part of the tubular knitted fabric is bent and folded back, creased, or distorted, resulting in a nonuniform heatsetting effect and also in a phenomenon detrimental to its deknittability. These drawbacks can be prevented by the regulating pieces 8 and 14 of the present invention. In order to be maintained stably on the supporting rods, the regulating pieces 8 and 14 should preferably be in a straight line with the base of the supporting rods. As shown in FIG. 1, the stitch loop density regulating piece of the invention is provided in two places, one at the beginning of feeding, and the other immediately before a heat-setting device.

Referring to FIG. I, the knitted fabric 1 rendered in a normal state by the regulating piece 8 advances via supporting rods 9 and 9', passes through feed rollers 2 and 3, and finally arrives at hot toothed rollers 4 and 5. Midway in this course, the fabric is imparted a uniform stretching force in the wale direction by a tension device 11 suspended via guide rods 10 and 10' of the fabric tension controlling mechanism. In the present invention, the above-mentioned fabric tension-controlling mechanism is designed with special ingenuity, and this constitutes a principal part of the present invention. The details of it will be mentioned later.

The tubular knitted fabric 1 which has passed the supporting rod is again regulated in its shape by the regulating piece 14 and supporting rods and 15 which support said regulating piece 14, and is then introduced into the hot toothed rollers 4 and 5. The hot toothed rollers are maintained at predetermined high temperatures, and while holding the tubular knitted fabric with a predetermined pressure, heat-set the fabric 1 and deliver a heat-set, crimped fabric 6. One of the hot rollers 4 and 5 is positively driven, while the other, being in contact with the former, is rotated in the opposite direction.

Now, the tension controlling mechanism will be described in greater detail.

A special apparatus is needed to place a running stretchable tubular knitted fabric under a predetermined tension in a continuous manner. If a tubular knitted fabric is merely moved at a predetermined speed between the feed rolls 2 and 3 and the hot toothed rolls 4 and 5, it cannot be maintained at all under a constant tension, being loosened at one time and being subjected to an excessive tension at another time, since the density of the tubular knitted fabric itself is not uniform. This problem is solved by on-off controlling or proportional controlling of the surface velocity of the feed rolls 2 and 3 and the hot toothed rolls 4 and 5, but the latter-mentioned method of controlling the surface velocity of the hot toothed rolls 4 and 5 is not preferable, because the hot toothed rolls 4 and 5 should always be rotated at a predetermined velocity to give a uniform heat-setting effect. For the foregoing reasons, the desired objects can be achieved by controlling the surface velocity of the fabric feed rolls 2 and 3. In FIG. 1, the tension device 11 is placed on the tubular knitted fabric 1 tensioned between the feed rolls 2 and 3 and the hot toothed rolls 4 and 5. As a matter of course, tension to be given to the fabric 1 can be adjusted by the tension device 11. In the present invention, the weight of the tension device 11 should be so selected that it is most suitable for manufacture of knit-molded type crimped yarns. But as the density of the advancing tubular knitted fabric 1 is not uniform, the stretching or contraction occurs accordingly. In accordance with the up-and-down movement of the tension device 11, magnetic relays 16 and 17 provided at the upper and lower ends of two rails 12 and 13 are actuated, and then a magnetic clutch 7 secured to a driving shaft of the feed roll 3 is actuated to effect the rotation and stopping of the feed rolls. To state it more specifically, a portion of a tubular knitted fabric which is low in density lowers the tension device 11. Thus, the magnetic relay 17 on the off side connected to the lower ends of the rails 12 and 13 is actuated, and the magnetic clutch 7 is opened to stop the rotation of the feed rolls. When thereafter the tension device 11 rises and comes to the upper ends of the rails 12 and 13, a magnetic relay 16 actuates the magnetic clutch 7, and the feed rolls again rotate. Repetition of this action makes it possible to obviate the above-mentioned phenomenon, and the tubular knitted fabric is fed into hot toothed rolls always in a constant density.

As shown in FIG. 2, the tension device consists of a shaft 18, detachable curved members 19, detachable fixing members 20, detachable weights 21, and rotary bodies 22 for engagement with the rails. The curved member 19 is effective in expanding a passing tubular knitted fabric in the course direction, and the center of gravity of the tension device as a whole is situated in the middle of the shaft 18. The curved member 19 can be of a suitable length depending upon the width of a tubular knitted fabric to be fed, and is fixed at both ends by the fixing members 20. The weight 21 is also variable according to the type and processing conditions of a tubular knitted fabric to be fed.

Another type of the tension-imparting means is shown in FIG. 3. A surface of the roller of this means which comes into contact with a tubular knitted fabric should preferably be a curved surface 23 for expansion of the fabric 1 in the course direction. It is also preferable that the center of gravity of the tension device as a whole should be situated on a perpendicular line extending on a vertex of an isosceles triangle drawn down the central line X-X of the roller 23 which is a base of the triangle. The upper and lower magnetic relays are actuated by a portion 26 extended from one end of the central axis of the rotary roller 23.

Summarizing the foregoing description, the present invention has for its object the provision of uniform crimps and increased crimp fastness by imparting a uniform heat-setting effect to a tubular knitted fabric in the manufacture of knitmolded type crimped yarns from thermoplastic yarns. To achieve this object, the following two technical measures have been taken.

Each of the yarns that constitute a tubular knitted fabric is originally formed in loops. When the tubular knitted fabric is placed under tension in the wale direction, the fabric contracts in the course direction, resulting in the deformation of the loops of each yarn. In order to rectify it, a stitch loop density regulating piece as shown in FIG. 4 is inserted according to the present invention into a tubular knitted fabric as shown in FIG. 5. As shown in the drawing, this density regulating piece expands the tubular knitted fabric. The expansion can be regulated by the shape of the density regulating piece, but it is preferable that the expansion should be of a degree -90 percent of the width in the course direction at the time of the knitting. If this is realized before hot toothed rolls 4 and 5, each of the loops of yarns that constitute the tubular knitted fabric becomes uniform, and rearranged in the most preferable form. Advantageously, when the tubular knitted fabric is expanded, each of the yarns in loops is imparted a tension in the course direction. FIG. 5 (a) indicates that the tubular knitted fabric is tensioned in the wale direction, and therefore, it contracts to some degree in the course direction. Since the tubular knitted fabric in this state is expanded outwardly by the stitch loop density regulating piece, each of the yarns in loops is naturally subjected to a tension in the course direction. As shown in FIG. 5(b), the width of the tubular knitted fabric is spread while not being tensioned in the wale direction. In other words, when a stitch loop density regulating piece is inserted in the fabric, the width of the fabric is spread during which time tension in the course direction occurs, and the fabric contracts in the wale direction since the fabric is not under tension in the wale direction. The use of a stitch loop density regulating piece in the'present invention serves firstly to return each of the loops of yarns that constitute the tubular knitted fabric to the original state, and secondly to impart to the yarns a tension in the course direction. It is most important that the stitch loop density regulating piece should be inserted into a tubular knitted fabric just before the hot toothed rolls 4 and S.

In order to achieve the objects of the present invention, it is also necessary to solve a problem of tension in the wale direction. In other words, according to the invention, a running tubular knitted fabric is subjected to a tension in the wale direction, and the tension is continuously maintained constant. The tubular knitted fabric has no uniform loop density, and contains both coarse and compact portions. When, therefore, such knitted fabric is subjected to tension, it is stretched non-uniformly, and hence arises a necessity of regulating it. This has been achieved according to the present invention by suspending a tension device from a running tubular knitted fabric between feed rolls and hot toothed rolls whereby the surface velocity of the feed rolls is controlled in response to the up-and-down movement of the tension device caused by changes in density of the tubular knitted fabric. Tension to be exerted on the tubular knitted fabric can be freely regulated by changing the weight of said tension device.

As shown in an embodiment of the invention as represented by FIG. 1, both the method I. mentioned above, i.e., the use of a stitch loop density regulating piece, and the method 2), Le, adjustment of stretch and contraction of a running tubular knitted fabric are employed at the same time. Since the fabric immediately upstream of the hot toothed rolls is under tension in the course and wale directions. there will be no deformation of the loops of the fabric as it enters the hot toothed rolls. Under these conditions. the fabric passes through the hot toothed rolls and is accurately molded according to the pattern of teeth with the entire stress of the teeth concentrated on the bending portions of the yarn. The fabric. being meshed with the hot toothed rolls, is heat-set in this condition. Thus, the heat-treated crimped yarns take three-dimensional plural wave configurations and show a large crimp development. Furthermore, the cross section of each of the filaments which constitute the crimped yarn either retains its original shape or is deformed at random. Therefore, a fabric obtained from such filaments exhibits an excellent boucle effect and develops a unique luster effect. Since according to the presert invention, the arrangement of yarn loops is maintained as uniform as possible, and in this state, they are heat set, the tubular knitted fabric is completely free from fold-back portions or creased portions. This means a remarkable improvement in deknitting and winding efficiency. As a natural result, it is possible to obtain crimped yarns of knit-molding methods free from such defects as filament breakage and fuzzing.

As shown in Table 1 below, the crimped yarns of knit-molding type obtained in accordance with the present invention have three-dimensinal plural wavy configuration and exhibit an excellent crimp fastness, while crimped yarns obtained by the prior art method have two-dimensional single wavy configuration and show a poor crimp fastness.

TABLE I Prior art Present invention W Shape oferimps..... Single wave two di- Plural wave three dimenslonel. menslonal. Shape of cross-section Original shape Mixture of original of filaments. agape and deformed s ape. Shape of the stlsde oi the Uniform Non-uniform.

. Excellent.

EXAMPLE l A semidulllOO-denier, 48-filament polyethylene terephthalate filament yarn was knitted on a circular knitting machine with 174 needles and a cylinder, 2 inches in diameter at 515 r.p.m. of the cylinder. The stitches of the thus knitted cloth were heat set with a knit heat set device of the present invention as seen in FIG. I. At this time, the surface speed, surface temperature, and compression force of hot toothed rolls 4 and 5 were set respectively to 4.5 m./min., 2l0 C. and 50 kg. (equivalent to a yarn speed of 3,500 m./min.), and the gross weight of tension device 11 was set to 400 g. Knit loop density regulating pieces 8 and 14 used in this process were of a plastic material in the form of an isosceles triangle. 60 mm. in base length, 70 mm. in height, 4 mm. in maximum thickness and 1 mm. in minimum thickness.

The thus stitch-set knitted cloth did not have such folds, wrinkles, kinks, etc., which would otherwise lower deknitting and winding performance of the knitted cloth. Deknitting and winding efficiency was remarkably enhanced. As a natural result, a three-dimensional crimp yarn of knit-molding methods was obtained, which had no yarn defects such as broken filaments, fuzzing, and so forth and which had a remarkably high crimp fastness. The test results are given in Table 2.

TABLE 2 Properties of processed yarn Tensile Yarn crimp Residual strei th elongation shrinkage Apparatus (gjfiL) percent percent Conventional apparatus No. l. 3. 69 36. 2 2 57 Conventional apparatus No. 2. 3. 86 38. i i. 42 Conventional apparatus No. 8. 3. 38 46. l 0. Apparatus of present invention. 2. 92 82. 1 0. 58 Appnratusof present invention 3. 80 69. l 0 53 Note I Conventional apparatus No. I

l knitted cloth heal set with steam at l30C., 30 min. in the relaxed state.

Conventional apparatus No. 2

= knitted cloth hcnt set with steam at I30 (1. 30 min. under linear tension.

Conventional apparatus No. 3

=knitted cloth heat set in the dry state at 220 C., 30 min.

under linear tension.

and

The uppurutus ofrhe present invention knitted cloth hcul set at is surface temperature of the toothed rolls of 200C. by the same process as in Example I.

Note 2 Methods of testing for yum crimp elongation and residual shrinkage of yttrn are described below.

Yum crimp clnngulion percent:

Collect in specified number ol'crimp yarns and carry out heat treatment 10 minutes in relaxed slate at the boil. followed by dcwutering und uir-drying lrculmenl. Apply a load of 2 mg. per denier for 2 minutes to lcl the specimen hung down. Let the length of the specimen at that time he lo. One minute after the unlonding. apply it load of 0.2 g. per denier for 2 min. Let the length of the specimen be I. Thus. yarn crimp elongation (I I'Io)/Io X I00 ('i- Residual shrinkage:

Collect in specified number of crimp yarns. Apply it load of 0.2 g. per denier [or 2 min. Let the length of the specimen u! lhul time he Il. Then, hour the specimen for 30 minutes in relaxed slate at the boil, followed by dcwutering und uir drying Ireulmcnl.

Aguin apply it loud of0.2 g. per denier for 2 min. and let the length ol'lhc specimen at thistimc be I2. Thus. Residual shrinkage (I. hill X [00 (5).

As clearly seen in Table 2, the yarn crimped by use of the apparatus of this invention has a remarkably higher crimp elongation and a remarkably lower residual shrinkage as compared with yarn prepared using conventional apparatus.

This shows that the apparatus of this invention is remarkably excellent in heat setting tubular knit cloth and providing it with an exceedingly high crimp permanence. Crimp elongation and residual shrinkage of yarn in Table 2 are characteristics capable of evaluating the degree of heatsetting. High crimp elongation and low residual shrinkage mean an excellent heat-setting.

EXAMPLE 2 A semidull ISO-denier. 30-filament polyethylene terephthalate filament yarn was knit on a circular knitting machine with 174 needles and a cylinder, 2 inches in diameter at a cylinder r.p.m. of 5 l 5. The stitches of the thus knit cloth were heat set with a knit heat set device of the present invention as seen in HO. 1. At this time, the surface speed, surface temperature. and compression force of hot toothed rolls 4 and 5 were set respectively to 5 m./min., 220 C. and 60 kg., and the gross weight of tension device 11 was set to 600 g. Knit loop density regulating pieces 8 and I4 are of the same grade as in Example l. The thus stitch-set knitted cloth did not have such folds, wrinkles, kinks, etc., which tend to lower deknitting and winding performance of the knit cloth. Deknitting and winding efficiency were remarkably increased. As a result, an excellent crimp yarn without broken filaments or fuzzing was obtained. The test results are givcn in Table 3.

This 3 Properties of processed yarn Tensile Yarn crimp Residual strength elongation shrinkage Apparatus (g./d.) percent percent Conventional apparatus No. 1.". 3. 70 35. 4 2. 60 Conventional apparatus No. 2.... 3. 80 39. 6 l. 52 Conventional apparatus No 3. 3. 40 45. 2 0. 98 Apparatus of present invention--- 3. 65 92. 1 0. 32

NorE.-Heat-settlng using conventional apparatus Nos. 1, 2, and 3 is the same as in Example 1.

We claim:

1. An apparatus for holding and setting the stitches of a deknittable tubular knitted fabric composed of thermoplastic filaments which comprises in combination a pair of feed rolls for feeding said tubular knitted fabric; a pair of hot toothed rolls for heat crimping said tubular knitted fabric downstream from said pair of feed rolls; tension means positioned between said pair of feed rolls and said pair of hot toothed rolls and suspended from said tubular knitted fabric to apply tension thereto in the wale direction, said tension means being vertically movable in response to variations in the density of said tubular knitted fabric; a stitch loop density regulating piece situated immediately upstream of said pair of hot toothed rolls within said tubular knitted fabric, said stitch loop density regulating piece having the shape of an isosceles triangle, the vertex of which is opposed to the running direction of said tubular knitted fabric; a pair of support rods located between said stitch loop density regulating piece and said pair of hot toothed rolls on either side of said tubular knitted fabric to support said stitch loop density regulating piece in the path of said tubular knitted fabric; and control means responsive to the vertical movement of said tension means to control the speed of said pair of feed rolls.

2. The apparatus of claim 1 further comprising a second stitch loop regulating piece located immediately upstream of said pair of feed rolls within said tubular knitted fabric, said second stitchloog density regulating piece having the shape of an isosceles triangle, the vertex of which is opposed to the running direction of said tubular knitted fabric; and a second pair of support rods located between said second stitch loop regulating piece and said pair of feed rolls on either side of said tubular knitted fabric to support said second stitch loop regulating piece in the path of said tubular knitted fabric. 

1. An apparatus for holding and setting the stitches of a deknittable tubular knitted fabric composed of thermoplastic filaments which comprises in combination a pair of feed rolls for feeding said tubular knitted fabric; a pair of hot toothed rolls for heat crimping said tubular knitted fabric downstream from said pair of feed rolls; tension means positioned between said pair of feed rolls and said pair of hot toothed rolls and suspended from said tubular knitted fabric to apply tension thereto in the wale direction, said tension means being vertically movable in response to variations in the density of said tubular knitted fabric; a stitch loop density regulating piece situated immediately upstream of said pair of hot toothed rolls within said tubular knitted fabric, said stitch loop density regulating piece having the shape of an isosceles triangle, the vertex of which is opposed to the running direction of said tubular knitted fabric; a pair of support rods located between said stitch loop density regulating piece and said pair of hot toothed rolls on either side of said tubular knitted fabric to support said stitch loop density regulating piece in the path of said tubular knitted fabric; and control means responsive to the vertical movement of said tension means to control the speed of said pair of feed rolls.
 2. The apparatus of claim 1 further comprising a second stitch loop regulating piece located immediately upstream of said pair of feed rolls within said tubular knitted fabric, said second stitch loop density regulating piece having the shape of an isosceles triangle, the vertex of which is opposed to the running direction of said tubular knitted fabric; and a second pair of support rods located between said second stitch loop regulating piece and said pair of feed rolls on either side of said tubular knitted fabric to support said second stitch loop regulating piece in the path of said tubular knitted fabric. 